This invention relates to a hydrophilic coating including diamond-like carbon (DLC) provided on (directly or indirectly) a substrate of glass, plastic, or the like, and a method of making the same. More particularly, this invention relates to a DLC inclusive coating that is exposed to at least ultraviolet (UV) radiation in order to cause the coating to either become hydrophilic or become more hydrophilic (i.e., to cause contact angle xcex8 of the coating to decrease).
It is often desirable to provide a hydrophilic coating (e.g., anti-fog coating) on a substrate such as an automotive windshield, automotive window, automotive mirror, architectural mirror, bathroom mirror, or the like. Such coatings may reduce the likelihood of water drops deposited on the substrate taking globular shape(s), thereby enabling visibility to be improved. In other words, hydrophilic coatings function to reduce bead-like condensation on substrate surfaces (e.g., on the interior surface of an automotive windshield or window). A hydrophilic coating can reduce the formation of many tiny droplets of liquid, which can scatter light, on a surface (i.e., make condensation on a surface film-wise as opposed to droplet-wise).
Unfortunately, certain hydrophilic coatings are not as durable and/or hard as would otherwise be desired and thus are not efficient from a practical point of view for applications such as automotive windshields and/or other types of windows.
In view of the above, it is apparent that there exists a need in the art for (i) a coated article (e.g. coated glass or plastic substrate) having hydrophilic properties, and a method of making the same, and/or (ii) a protective hydrophilic coating for window and/or mirror substrates that is somewhat resistant to scratching, damage, or the like.
It is a purpose of different embodiments of this invention to fulfill any or all of the above described needs in the art, and/or other needs which will become apparent to the skilled artisan once given the following disclosure.
An object of this invention is to provide a durable coated article that it is less likely to attract or be affected by bead-like liquid condensation. Exemplary applications to which such hydrophilic coating(s) may be applied include, for example without limitation, automotive windshields, automotive backlites (i.e., rear vehicle windows), automotive side windows, architectural windows, mirrors, etc.
Another object of this invention is to provide a scratch resistant hydrophilic coating for use in conjunction with a coated article.
Another object of this invention is to form or provide a hydrophilic coating by doping diamond-like carbon (DLC) with at least one polar inducing dopant(s) such as, for example, boron (B) and/or nitrogen (N). In certain embodiments, the atomic percentage of the polar inducing dopant(s) (e.g., B and/or N dopants, but not including H dopants that may or may not be added because H is not a polar inducing dopant) is no greater than about 10%, more preferably no greater than about 5%, and most preferably no greater than about 4%. A polar inducing dopant is a dopant that causes DLC to become more graphitic (e.g., cause more sp2 bonds), as opposed to more tetrahedral (i.e., more sp3 bonds). Polar inducing dopant(s) tend to cause the DLC inclusive layer to be more polar, which in turn increases surface energy and thus provides for a more hydrophilic coating.
Another object of this invention is to provide a coated article, wherein a layer of the coating includes both sp2 and sp3 carbon-carbon bonds and has a wettability W with regard to water of at least about 700 mN/m, more preferably at least about 750 mN/m, and most preferably at least about 800 mN/m. This can also be explained or measured in Joules per unit area (mJ/m2).
Another object of this invention is to cause contact angle xcex8 of a DLC inclusive layer or coating to decrease due to ultraviolet (UV) exposure. The contact angle before such exposure may or may not be hydrophilic, but after said exposure in certain example embodiments the post-UV contact angle xcex8 is less than about 20 degrees, more preferably less than about 15 degrees, even more preferably less than about 10 degrees, and even more preferably less than about 8 degrees.
Another object of this invention is to provide a coated article, wherein a layer of the coating includes both sp2 and sp3 carbon-carbon bonds and has a surface energy xcex3c of at least about 24 mN/m, more preferably at least about 26 mN/m, and most preferably at least about 28 mN/m.
Another object of this invention is to provide a coated article, wherein a DLC inclusive layer of the coating has an initial (i.e. prior to being exposed to environmental tests, rubbing tests, acid tests, UV tests, or the like) water contact angle xcex8 of no greater than about 10 degrees, more preferably no greater than about 8 degrees, even more preferably no greater than about 6 degrees, and most preferably no greater than about 4 degrees. The article""s initial contact angle xcex8 may be as low as 1-3 degrees in certain embodiments. In certain embodiments the article""s contact angle may increase over time upon exposure to environmental elements (as graphitic sp2 Cxe2x80x94C bonds wear off) while in other embodiments the article""s contact angle may decrease over time upon such exposure.
Another object of this invention is to provide a hydrophilic DLC inclusive layer for coating a substrate. In at least one portion of the layer no more than about 70% of the bonds in that portion of the layer are of the sp3 type, and more preferably no more than about 60% of the bonds are of the sp3 type. A substantial portion of the remainder of the bonds may be of the graphitic or sp2 type. The bonds in the layer may include, for example, carbon-carbon (Cxe2x80x94C) bonds, carbon-nitrogen (Cxe2x80x94N) bonds, carbon-boron (Cxe2x80x94B) bonds, and/or carbon-hydrogen (Cxe2x80x94H) bonds. The sp3 type bonds (e.g., Cxe2x80x94C bonds) function to increase the hardness and scratch resistance of the coating, while the graphitic sp2 type bonds (e.g., Cxe2x80x94C, Cxe2x80x94N and/or Cxe2x80x94B bonds) cause the coating to be more hydrophilic and have a lower contact angle.
Another object of this invention is to provide a coating which can make accumulated condensation form in a more film-wise manner; as opposed to a droplet-wise manner.
Still another object of this invention is to form amine (NH2) functional groups near the surface of a hydrophobic coating or layer so as to enhance hydrophilicity.
Yet another object of this invention is to fulfill one or more of the above listed objects and/or needs.
Certain example embodiments of the instant invention fulfill one or more of the above-listed objects or needs by providing a coated glass article comprising:
a glass substrate;
a layer comprising diamond-like carbon (DLC) with sp3 carbon-carbon bonds provided on said glass substrate; and
wherein said layer comprising DLC is ultraviolet (UV) radiation exposed so as to cause the layer to have a contact angle xcex8 with a drop of water thereon of no greater than about 20 degrees.
Other example embodiments of the instant invention fulfill one or more of the above-listed objects or needs by providing a method of making a coated article, the method comprising:
ion beam depositing a diamond-like carbon (DLC) inclusive layer on a substrate; and
exposing the DLC inclusive layer to ultraviolet (UV) radiation in a manner sufficient to cause a contact angle xcex8 of the DLC inclusive layer to decrease by at least about 20%.
Still further example embodiments of the instant invention fulfill one or more of the above-listed objects and/or needs by providing a coated article comprising a DLC inclusive layer supported by a glass substrate, wherein the DLC inclusive layer has a contact angle xcex8 less than or equal to 10 degrees.
This invention will now be described with respect to certain embodiments thereof, along with reference to the accompanying illustrations.